Seat back



FIG. 1 is a perspective view of a seat back showing my new design;

FIG. 2 is another perspective view thereof;

FIG. 3 is a front elevational view thereof;

FIG. 4 is a rear elevational view thereof;

FIG. 5 is a left side elevational view thereof;

FIG. 6 is a right side elevational view thereof;

FIG. 7 is a top plan view thereof;

FIG. 8 is a bottom plan view thereof;

FIG. 9 is an enlarged view of portion 9 shown in FIG. 1; and,

FIG. 10 is an enlarged view of portion 10 shown in FIG. 2.

The broken lines in the drawings depict portions of the seat back that form no part of the claimed design. 

CLAIM The ornamental design for a seat back, as shown and described. 